1. Technical Field
The present invention is directed toward corrugators, and more particularly toward corrugators for making corrugated plastic tubing.
2. Background Art
A well known method for manufacturing corrugated pipes is to extrude a tube of thermoplastic from a head and then conform that tube to the interior of a corrugated mold tunnel formed by mold blocks. The mold blocks typically come in pairs and mate together to form a portion of the mold tunnel, and the thermoplastic is either blown into its shape (by pressure created within the mold tunnel) or by vacuum (where vacuum draws the air from around the mold tunnel).
Structures which have been used in the vacuum method of manufacture are illustrated in U.S. Pat. Nos. 4,319,872, 4,439,130, and 4,718,844. These patents all address the problem of drawing a uniform, strong vacuum around the entirety of the mold blocks which are continually moving during the molding process, As can be seen from these structures, it is difficult to inexpensively form any such mold block.
Certain problems naturally occurring in all such machines are exaggerated in machines which are used to make larger diameter tubes (for example, up to four feet in diameter and more).
Conforming the thermoplastic to the larger diameter mold blocks with a uniformity of wall thickness can be difficult.
Moving and properly aligning multiple mold blocks is also naturally more difficult with larger diameter mold blocks due to the mere size and weight of the parts involved and their interaction with other components. In clamshell type machines, for example (with the mold blocks supported on a carriage on one side), any forces incurred on the other side of the mold blocks naturally involves a larger moment arm about the carriages, with the result being that such structures can be more susceptible to "sawtooth" type arrangements through the mold tunnel, with successive mold blocks being tilted slightly rather than perfectly aligned with the axis of the mold tunnel.
The present invention is directed toward overcoming one or more of the problems set forth above.